1. Field of the Invention
The invention relates to the use of free-flowing iron oxides with 50 to 73 wt. % iron.
2. Description of the Prior Art
Particulate magnetites produced by precipitation processes from aqueous solutions have been known for a long time. In U.S. Pat. No. 802,928, the production of magnetite by the precipitation of iron(II) sulphate with an alkaline component and subsequent oxidation with air is described. Numerous other applications relating to the production of magnetites by the precipitation process were subsequently filed. The iron oxides produced were initially used for the production of all types of paints. The particular advantage of magnetites compared with organic dyes and carbon black lies in their very much better weathering resistance, so that paints of this type can also be used outdoors. Furthermore, precipitation magnetites are used for colouring concrete mouldings, such as concrete paving stones or concrete roofing tiles. Magnetites have also been used for some time in electrophotography for the production of toners.
Magnetites produced by the precipitation process are preferably used to produce toners for copiers with single-component toners. The magnetic toner used for this purpose must have various general properties. As copiers and printers continue to be developed and improved, the requirements of the magnetic toner and, consequently, of the magnetite used for it, have become increasingly high. The latest generation of printers achieves a resolution of more than 600 dpi (dots per inch), which has led to the development of fine particle size toners with a very narrow particle size distribution. This means that the magnetites required for them must have a very narrow particle size distribution. Moreover, a particular particle size is required so that a homogeneous distribution of the magnetite particles in the finished toner is ensured. The magnetites available on the market for the production of toners are powders which meet these requirements. However, these powdered precipitation magnetites have poor flow properties. Metering of the powdered magnetite is therefore difficult and labour-intensive. Moreover, the powdered pigments tend to give off dust. For these reasons, granules would be more suitable than powders. The disadvantage of granules, on the other hand, is that they have to be dispersible. Hard, strong, readily transported and metered, free-flowing granules are usually poorly dispersible. Soft granules are readily dispersible, but not usually transportable, and disintegrate back into powders when handled.
In U.S. Pat. No. 5,401,313, among other things, special pigment granules are described which are produced from the corresponding powders with at least one additive to modify the surface charge and at least one dispersion-promoting additive. These granules may also be used in magnetic toner compositions.
The object of the present application was therefore to provide magnetic iron oxide-containing granules that may be used in toners, printing inks and inks and that have the following properties:
good flow properties PA1 high colour intensity PA1 largely dust-free PA1 readily metered PA1 readily transported in metering equipment PA1 good dispersibility PA1 formulation compatibility. PA1 spray granulation PA1 disk granulation PA1 press granulation. PA1 An aqueous dispersion of the magnetic iron oxide-containing compound is produced by breaking up a filter cake using a high-speed stirrer or continuous flow disperser units by the rotor-stator principle. This dispersion contains 150-500 g/l of magnetite. PA1 The binder is added to this dispersion in liquid form (either pure or dissolved in a suitable solvent). PA1 This dispersion is mixed for 10 min to 240 min by stirring, pumping or passing through the continuous flow disperser unit, so that the binder is homo-geneously distributed in the dispersion. PA1 The finished dispersion is sprayed in a nozzle or disk spray drier. The exhaust gas temperature should be 110-140.degree. C. The speed of the disk is selected such that the desired granule size is obtained (depends on the throughput and the size of the spray drier). PA1 The Fe(II) content is determined by titration with KMnO.sub.4 by means of a Memotitrator (Mettler DL-70). Fe(III) is determined in the same way with TiCl.sub.3. The total iron content is calculated from the two individual values and the weighed quantity. The contents of the two standard solutions are determined daily. PA1 The granule sample was first passed through a sieve with a 2.5 mm mesh size. 50 g thereof were weighed into a sieve jar (diameter=76 mm; height=94 mm) with an intermediate sieve plate with a 1 mm mesh size. The sieve jar with the weighed portion was placed in a collecting jar with a 102 mm diameter and a height of 163 mm. At the bottom of the collecting jar was a bayonet seal. This was used to place the jar on a tamp volumeter according to DIN/ISO 787, part 11 and tamping was performed up to 400 times. If the flow properties are very good, the number of tamping strokes may be reduced to up to 25. The flow properties were expressed as wt. % of residue on the 1 mm sieve in the sieve jar. ##EQU1##
It was possible to achieve this object with specific granules.